CN105207270B - Improve the inverter power control method for coordinating of grid-connected voltage out-of-limit - Google Patents

Abstract

The invention discloses an inverter power coordination control method for improving photovoltaic grid-connected voltage exceeding the limit, and relates to the technical field of devices or methods for adjusting electric variables. The method includes the following steps: 1) Real-time detection of the voltage U _S at the grid-connected point during the operation of the photovoltaic grid-connected inverter, and the upper voltage U _max at the photovoltaic grid-connected point is a known quantity; 2) If U _S ≤ U _max , the inverter sends active power P _PV in the MPPT control mode; 3) If U _S > U _max , the inverter starts the power coordination control mode to maintain the grid-connected point voltage at the upper voltage limit U _max . The method can make the voltage output by the photovoltaic inverter respond to the voltage change of the grid-connected point in real time, dynamically distribute the active power and reactive power of the photovoltaic inverter, ensure that the voltage of the photovoltaic grid-connected point is always maintained at or below its upper limit, and reduce the number of inverters. The number of quit operations enables photovoltaic power generation to have significant and flexible voltage regulation capabilities.

Description

Inverter power coordination control method to improve photovoltaic grid-connected voltage exceeding the limit

technical field

The present invention relates to the technical field of devices or methods for adjusting electrical variables, in particular to an inverter reactive power adjustment control method for preventing photovoltaic grid-connected voltage from exceeding the limit.

Background technique

With the increasingly prominent energy crisis, renewable energy is more and more popular, especially solar energy, which is clean, pollution-free, widely distributed and easy to exploit. Photovoltaic power generation is rapidly growing globally as a form of efficient use of solar energy. Photovoltaic grid connection can be directly connected to the grid on the low-voltage side or connected to the grid after a step-up transformer. After the photovoltaic power source is incorporated into the distribution network, the original single power source radial structure becomes a multi-power source structure, which changes the direction and magnitude of the original power flow. getting bigger. It is necessary to solve the problem that the grid-connected point voltage exceeds the limit after photovoltaic grid-connected. The existing main technical means to improve the voltage limit of the distribution network are: transformer on-load voltage regulation, capacitor bank compensation, active filter (APF) compensation, static var generator (SVG) compensation, etc. These technical means need to be increased Hardware investment is not suitable for all distribution networks connected to photovoltaics.

Contents of the invention

The technical problem to be solved by the present invention is to provide an inverter reactive power adjustment control method to prevent photovoltaic grid-connected voltage from exceeding the limit. The method can make the voltage output by the photovoltaic inverter respond to the voltage change of the grid-connected point in real time, and dynamically allocate The active power and reactive power of the inverter ensure that the voltage of the photovoltaic grid-connected point is always maintained at or below its upper limit, reducing the number of times the inverter is out of operation, and enabling photovoltaic power generation to have significant and flexible voltage regulation capabilities.

In order to solve the above technical problems, the technical solution adopted by the present invention is: an inverter power coordination control method for improving photovoltaic grid-connected voltage exceeding the limit, which is characterized in that the method includes the following steps:

1) During the operation of the photovoltaic grid-connected inverter, the voltage U _S at the grid-connected point is detected in real time, and the upper voltage limit U _max at the photovoltaic grid-connected point is a known quantity;

2) If U _S ≤ U _max , the inverter sends active power P _PV in MPPT control mode;

3) If U _S > U _max , the inverter starts the power coordination control mode, so that the grid-connected point voltage is maintained at the voltage upper limit U _max .

A further technical solution is: the power coordinated control mode specifically includes the following steps:

If U _S > U _max , the inverter starts the power coordination control mode, and records the current active power P _PV generated by the inverter. At this time, the reactive power Q′ _PV generated by the inverter is

The active power P _PV generated by the inverter and the reactive power Q′ _PV generated by the inverter calculated by formula (1) are used as the reference input value of the active and reactive power of the inverter at the next moment, and the inverter is calculated PQ control;

Detect the grid-connected point voltage U _S of the inverter at the next moment. If it does not exceed the upper voltage limit U _max at the photovoltaic grid-connected point, the inverter will keep running in the current mode. During this process, if the active power P generated by the current inverter _PV continues to increase, then reduce the reactive power Q′ _PV sent according to formula (1);

If the grid-connected point voltage U _S still exceeds the upper voltage limit U _max at the photovoltaic grid-connected point, then reduce the active power P _PV generated by the inverter, and increase the reactive power Q′ _PV generated according to formula (1);

When Q′ _PV is no longer negative, that is, when the inverter needs to actually generate reactive power, if the voltage of the grid-connected point exceeds the upper limit at this time, only the active power P _PV generated will be reduced to maintain the voltage of the grid-connected point at the upper voltage limit U at _max .

The further technical solution is: the reactive power that the inverter can use is

When Q _PV > 0, the inverter emits reactive power, and the grid-connected point voltage will increase even more at this time, so the inverter should absorb reactive power, that is, emit negative reactive power

The current PP _PV and the Q′ _PV calculated by formula (3) are used as the reference input value of the active and reactive power of the inverter at the next moment, and the PQ control is performed on the inverter.

A further technical solution is: the determination method of the inverter active power reduction ΔP _PV is as follows:

The active power P _PV and reactive power Q _PV generated by the inverter and the active power P _L and reactive power Q _L consumed by the load satisfy the following relationship

In formula (4): R is the line resistance connected to the photovoltaic power supply, X is the line reactance connected to the photovoltaic power supply, U _O is the distribution network voltage;

From formula (4) can get:

(U _O -U _S )U _S ＝(P _L -P _PV )R+(Q _L -Q _PV )X (5)

After starting the power coordinated control mode, if the grid-connected point voltage U _S still _exceeds the upper limit, the active power that the inverter should emit in order to make the grid-connected point voltage drop to the voltage upper limit U _max under the active power PPV generated by the inverter P′ _PV satisfies

(U _O -U _max )U _max =(P _L -P′ _PV )R+(Q _L -Q _PV )X (6)

The active power reduction ΔP _PV of the inverter can be obtained from the parallel formula (5) and formula (6):

The active power P′ _PV that the inverter should emit is

P′ _PV ＝P _PV +ΔP _PV (8)

The beneficial effect of adopting the above technical solution is that the method only needs to adjust the reactive power and active power value input by the photovoltaic grid-connected inverter, and can effectively solve the voltage limit problem at the grid-connected point, so that the voltage at the grid-connected point It is always maintained at or below the upper limit of the photovoltaic grid-connected point voltage, no additional hardware is required, the cost is low, and the control principle is simple, which can effectively reduce the number of times the inverter is out of operation, so that the photovoltaic power generation has a significant and flexible voltage regulation capability, thereby improving the photovoltaic power generation. Network performance, so that the photovoltaic power generation and distribution network can operate effectively.

Description of drawings

Figure 1 is a structural diagram of a single photovoltaic grid-connected distribution network system;

Among them: 1. Photovoltaic modules 2. Inverters 3. Distribution network.

detailed description

The technical solutions in the embodiments of the present invention are clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by persons of ordinary skill in the art without making creative efforts belong to the protection scope of the present invention.

In the following description, a lot of specific details are set forth in order to fully understand the present invention, but the present invention can also be implemented in other ways different from those described here, and those skilled in the art can do it without departing from the meaning of the present invention. By analogy, the present invention is therefore not limited to the specific examples disclosed below.

The invention discloses an inverter power coordination control method for improving photovoltaic grid-connected voltage exceeding the limit. The method only needs to adjust the reactive power and active power value input by the photovoltaic grid-connected inverter to effectively solve the grid-connected point The problem of voltage over-limit is solved, so that the voltage at the grid-connected point is always maintained at or below the upper limit of the voltage of the photovoltaic grid-connected point, no additional hardware is required, the cost is low, and the control principle is simple, which can effectively reduce the number of times the inverter is out of operation, so that photovoltaic power generation has a significant , Flexible voltage regulation capability, so as to improve the photovoltaic grid-connected performance, so that the photovoltaic power generation and distribution network can operate effectively.

Start the inverter for grid connection. In the initial stage of inverter operation, it operates in MPPT control mode, that is, only active power P _PV is issued. The inverter detects the grid-connected point voltage U _S in real time, and records the current active power P _PV and reactive power Q _PV (when no reactive power is generated, Q _PV is 0). The distribution network voltage U _O , the line reactance X connected to the photovoltaic power source, and the upper voltage limit U _max at the photovoltaic grid connection point are known quantities.

(1) If U _S ≤ U _max , the inverter sends active power in MPPT control mode.

(2) If U _S >U _max , the inverter starts the power coordination control mode, and records the current active power P _PV generated by the inverter. Usually, P _PV <S _PV , so the reactive power available to the inverter can be obtained as

When Q _PV > 0, the inverter sends out reactive power, and the grid-connected point voltage will increase even more at this time, so the inverter should absorb reactive power, that is, send out negative reactive power.

The current PP _PV and Q′ _PV calculated by formula (1) are used as the reference input value of the active and reactive power of the inverter at the next moment, and the PQ control of the inverter is carried out.

Detect the grid-connected point voltage of the inverter at the next moment, and if it does not exceed the upper voltage limit, the inverter will keep running in the current mode. During this process, if the active power _PPV continues to increase, the reactive power emitted is reduced according to formula (1).

If the voltage at the grid-connection point exceeds the upper limit, the active power _PPV generated is reduced at this time, and the reactive power generated is increased according to formula (1).

When Q′ _PV is no longer negative, that is, when the inverter needs to generate reactive power, if the grid-connected point voltage exceeds the upper limit at this time, only the active power PP _PV generated will be reduced.

The reduction ΔP _PV of active power PP _PV is determined by:

The active power P _PV and reactive power Q _PV generated by the inverter and the active power P _L and reactive power Q _L consumed by the load satisfy the following relationship

From formula (3) can get

(U _O -U _S )U _S ＝(P _L -P _PV )R+(Q _L -Q _PV )X (4)

After starting the power coordination control mode, if the grid-connected point voltage still exceeds the upper limit, the active power P′ that the inverter should emit in order to make the grid-connected point voltage drop to the voltage upper limit U _max under the active power P _PV generated by the inverter _PV meets

(U _O -U _max )U _max =(P _L -P′ _PV )R+(Q _L -Q _PV )X (5)

The active power reduction of the inverter can be obtained from the parallel formula (4) and formula (5):

The active power P′ _PV that the inverter should emit is

P′ _PV ＝P _PV +ΔP _PV (7)

Among them, U _O is the voltage of the distribution network, U _S is the voltage of the grid-connected point, R is the line resistance connected to the photovoltaic power supply, X is the line reactance connected to the photovoltaic power supply, S _PV is the injection capacity of the photovoltaic power into the distribution network, and PP _PV is the photovoltaic power supply. Active power sent to the distribution network, Q _PV is the reactive power sent by photovoltaics to the distribution network, P _L is the active power consumed by the load, and Q _L is the reactive power consumed by the load.

Claims (1)

1. An inverter power coordinated control method for improving photovoltaic grid-connected voltage exceeding the limit, characterized in that the method comprises the following steps: 1) During the operation of the photovoltaic grid-connected inverter, the voltage U _S at the grid-connected point is detected in real time, and the upper voltage limit U _max at the photovoltaic grid-connected point is a known quantity; 2) If U _S ≤ U _max , the inverter sends active power P _PV in MPPT control mode; 3) If U _S > U _max , the inverter starts the power coordination control mode, so that the grid-connected point voltage is maintained at the voltage upper limit U _max ; The power coordinated control mode specifically includes the following steps: If U _S > U _max , the inverter starts the power coordination control mode, and records the current active power P _PV generated by the inverter. At this time, the reactive power Q′ _PV generated by the inverter is <mrow><msubsup><mi>Q</mi><mrow><mi>P</mi><mi>V</mi></mrow><mo>&amp;prime;</mo></msubsup><mo>=</mo><mo>-</mo><msqrt><mrow><msubsup><mi>S</mi><mrow><mi>P</mi><mi>V</mi></mrow><mn>2</mn></msubsup><mo>-</mo><msubsup><mi>P</mi><mrow><mi>P</mi><mi>V</mi></mrow><mn>2</mn></msubsup></mrow></msqrt><mo>-</mo><mo>-</mo><mo>-</mo><mrow><mo>(</mo><mn>1</mn><mo>)</mo></mrow></mrow> The active power P _PV generated by the inverter and the reactive power Q′ _PV generated by the inverter calculated by formula (1) are used as the reference input value of the active and reactive power of the inverter at the next moment, and the inverter is calculated PQ control; among them, SP _PV is the injection capacity of photovoltaics into the distribution network; Detect the grid-connected point voltage U _S of the inverter at the next moment. If it does not exceed the upper voltage limit U _max at the photovoltaic grid-connected point, the inverter will keep running in the current mode. During this process, if the active power P generated by the current inverter _PV continues to increase, then reduce the reactive power Q′ _PV sent according to formula (1); If the grid-connected point voltage U _S still exceeds the voltage upper limit U _max at the photovoltaic grid-connected point, then reduce the active power P _PV generated by the inverter, and increase the reactive power Q′ _PV generated according to formula (1); When Q′ _PV is no longer negative, that is, when the inverter needs to actually generate reactive power, if the voltage at the grid-connected point exceeds the upper limit, only the active power generated will be reduced to maintain the voltage at the grid-connected point at the upper voltage limit U _max ; The reactive power that the inverter can utilize is <mrow><msub><mi>Q</mi><mrow><mi>P</mi><mi>V</mi></mrow></msub><mo>=</mo><msqrt><mrow><msubsup><mi>S</mi><mrow><mi>P</mi><mi>V</mi></mrow><mn>2</mn></msubsup><mo>-</mo><msubsup><mi>P</mi><mrow><mi>P</mi><mi>V</mi></mrow><mn>2</mn></msubsup></mrow></msqrt><mo>-</mo><mo>-</mo><mo>-</mo><mrow><mo>(</mo><mn>2</mn><mo>)</mo></mrow></mrow> When Q _PV > 0, the inverter sends out reactive power, and the grid-connected point voltage will increase even more at this time, so the inverter should absorb reactive power, that is, send out negative reactive power <mrow><msubsup><mi>Q</mi><mrow><mi>P</mi><mi>V</mi></mrow><mo>&amp;prime;</mo></msubsup><mo>=</mo><mo>-</mo><msqrt><mrow><msubsup><mi>S</mi><mrow><mi>P</mi><mi>V</mi></mrow><mn>2</mn></msubsup><mo>-</mo><msubsup><mi>P</mi><mrow><mi>P</mi><mi>V</mi></mrow><mn>2</mn></msubsup></mrow></msqrt><mo>-</mo><mo>-</mo><mo>-</mo><mrow><mo>(</mo><mn>3</mn><mo>)</mo></mrow></mrow> Use the current P _PV and Q′ _PV calculated by formula (3) as the reference input value of the active and reactive power of the inverter at the next moment, and perform PQ control on the inverter; The determination method of inverter active power reduction ΔP _PV is as follows: The active power P _PV and reactive power Q _PV generated by the inverter and the active power P _L and reactive power Q _L consumed by the load satisfy the following relationship <mrow><msub><mi>U</mi><mi>O</mi></msub><mo>=</mo><msub><mi>U</mi><mi>S</mi></msub><mo>+</mo><mfrac><mrow><mo>(</mo><msub><mi>P</mi><mi>L</mi></msub><mo>-</mo><msub><mi>P</mi><mrow><mi>P</mi><mi>V</mi></mrow></msub><mo>)</mo><mi>R</mi><mo>+</mo><mo>(</mo><msub><mi>Q</mi><mi>L</mi></msub><mo>-</mo><msub><mi>Q</mi><mrow><mi>P</mi><mi>V</mi></mrow></msub><mo>)</mo><mi>X</mi></mrow><msub><mi>U</mi><mi>S</mi></msub></mfrac><mo>-</mo><mo>-</mo><mo>-</mo><mrow><mo>(</mo><mn>4</mn><mo>)</mo></mrow></mrow> In formula (4): R is the line resistance connected to the photovoltaic power supply, X is the line reactance connected to the photovoltaic power supply, U _O is the distribution network voltage; From formula (4) can get: (U _O -U _S )U _S ＝(P _L -P _PV )R+(Q _L -Q _PV )X (5) After starting the power coordinated control mode, if the grid-connected point voltage U _S still _exceeds the upper limit, the active power that the inverter should emit in order to make the grid-connected point voltage drop to the voltage upper limit U _max under the active power PPV generated by the inverter P′ _PV satisfies (U _O -U _max )U _max =(P _L -P′ _PV )R+(Q _L -Q _PV )X (6) The active power reduction ΔP _PV of the inverter can be obtained from the parallel formula (5) and formula (6): <mrow><msub><mi>&amp;Delta;P</mi><mrow><mi>P</mi><mi>V</mi></mrow></msub><mo>=</mo><mo>-</mo><mrow><mo>(</mo><msub><mi>P</mi><mrow><mi>P</mi><mi>V</mi></mrow></msub><mo>-</mo><msubsup><mi>P</mi><mrow><mi>P</mi><mi>V</mi></mrow><mo>&amp;prime;</mo></msubsup><mo>)</mo></mrow><mo>=</mo><mo>-</mo><mfrac><mrow><mo>(</mo><msub><mi>U</mi><mi>S</mi></msub><mo>-</mo><msub><mi>U</mi><mi>O</mi></msub><mo>)</mo><msub><mi>U</mi><mi>S</mi></msub><mo>-</mo><mo>(</mo><msub><mi>U</mi><mrow><mi>m</mi><mi>a</mi><mi>x</mi></mrow></msub><mo>-</mo><msub><mi>U</mi><mi>O</mi></msub><mo>)</mo><msub><mi>U</mi><mrow><mi>m</mi><mi>a</mi><mi>x</mi></mrow></msub></mrow><mi>R</mi></mfrac><mo>-</mo><mo>-</mo><mo>-</mo><mrow><mo>(</mo><mn>7</mn><mo>)</mo></mrow></mrow> The active power P′ _PV that the inverter should emit is P' _PV =P _PV +ΔP _PV (8).